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Abstract:

A method and apparatus to detect load fluctuation of a wireless power
transmission are provided. A wireless power transmitter includes a
resonator configured to wirelessly transmit, to a target device, an
output power. The wireless power transmitter further includes a power
detector configured to detect a current of the output power. The wireless
power transmitter further includes a controller configured to detect a
change in the current, and to detect a target load based on the change in
the current. The target load includes a load of which the output power is
applied thereto.

Claims:

1. A wireless power transmitter comprising: a resonator configured to
wirelessly transmit, to a target device, an output power; a power
detector configured to detect a current of the output power; and a
controller configured to detect a change in the current, and detect a
target load based on the change in the current, and wherein the target
load comprises a load of which the output power is applied thereto.

2. The wireless power transmitter of claim 1, wherein the controller is
further configured to determine the output power.

3. The wireless power transmitter of claim 1, further comprising: a power
converter configured to output the output power.

4. The wireless power transmitter of claim 3, wherein the load is applied
to an output of the power converter.

5. The wireless power transmitter of claim 3, further comprising: a power
supply configured to apply, to the power converter, a voltage based on a
control of the controller.

6. The wireless power transmitter of claim 1, wherein the controller is
further configured to determine a state of a wireless power transmission
based on the target load.

7. The wireless power transmitter of claim 1, wherein, when the current
is less than a predetermined value, the controller is further configured
to terminate a charging of the target device.

8. The wireless power transmitter of claim 1, wherein the controller is
further configured to adjust the output power based on the target load.

9. The wireless power transmitter of claim 1, wherein the target load
comprises a sum of loads of target devices.

10. The wireless power transmitter of claim 1, wherein the current is
changed based on a change in a charging mode of the target device from a
constant current (CC) mode to a constant voltage (CV) mode.

11. The wireless power transmitter of claim 1, wherein the power detector
comprises: a first resistor in which the current flows; and a comparator
configured to output, to the controller, voltages applied to a first
terminal and a second terminal of the first resistor, wherein the
controller is further configured to detect the target load based on the
voltages and a resistance value of the first resistor.

12. The wireless power transmitter of claim 11, further comprising: a
power converter configured to output the output power, wherein the power
detector further comprises a second resistor comprising a first terminal
and a second terminal, the first terminal being connected to the first
terminal of the first resistor, and the second terminal being connected
to a positive terminal of the comparator, and a third resistor comprising
a first terminal and a second terminal, the first terminal being
connected to the second terminal of the first resistor and an input of
the power converter, and the second terminal being connected to a
negative terminal of the comparator.

13. A method of detecting a load in a wireless power transmission,
comprising: wirelessly transmitting, to a target device, an output power;
detecting a current of the output power; detecting a change in the
current; and detecting a target load based on the change in the current,
the target load comprising the load of which the output power is applied
thereto.

14. The method of claim 13, further comprising: determining a state of
the wireless power transmission based on the target load.

15. The method of claim 13, further comprising, when the current is less
than a predetermined value, terminating a charging of the target device.

16. The method of claim 13, further comprising adjusting the output power
based on the target load.

17. The method of claim 13, wherein the target load further comprises a
sum of loads of target devices.

18. The method of claim 13, wherein the current is changed based on a
change in a charging mode of the target device from a constant current
(CC) mode to a constant voltage (CV) mode.

19. The method of claim 13, further comprising: matching an impedance and
a resonant frequency of a source device to an impedance and a resonant
frequency of the target device.

20. A non-transitory computer-readable storage medium storing a program
comprising instructions to cause a computer to implement the method of
claim 13.

Description:

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims the benefit under 35 U.S.C. §119(e) of
U.S. Provisional Application No. 61/491,953, filed on Jun. 1, 2011, in
the United States Patent and Trademark Office, and claims the benefit
under 35 U.S.C. §119(a) of Korean Patent Application No.
10-2011-0078080, filed on Aug. 5, 2011, in the Korean Intellectual
Property Office, the entire disclosures of which are incorporated herein
by reference for all purposes.

BACKGROUND

[0002] 1. Field

[0003] The following description relates to a method and apparatus to
wirelessly transmit power, and more particularly, to a method and
apparatus to detect load fluctuation in a wireless power transmission.

[0004] 2. Description of Related Art

[0005] A wireless power refers to energy that is transferred from a
wireless power transmitter to a wireless power receiver through magnetic
coupling. Accordingly, a wireless power transmission and charging system
includes a source device and a target device. The source device may
wirelessly transmit a power, and the target device may wirelessly receive
a power. Here, the source device may be referred to as a wireless power
transmitter, and the target device may be referred to as a wireless power
receiver.

[0006] The source device includes a source resonator, and the target
device includes a target resonator. Magnetic coupling or resonance
coupling may be formed between the source resonator and the target
resonator.

[0007] A single source device may transmit power to a plurality of target
devices. In an example in which a plurality of target devices
simultaneously approach a resonator of a source device, or the plurality
of target devices are located within a range of the resonator, and power
is supplied to the source device, data collision may occur during an
operation for initial connection due to the plurality of target devices
requesting connection. Accordingly, a normal charging operation may not
be performed.

SUMMARY

[0008] In one general aspect, there is provided a wireless power
transmitter including a resonator configured to wirelessly transmit, to a
target device, an output power. The wireless power transmitter further
includes a power detector configured to detect a current of the output
power. The wireless power transmitter further includes a controller
configured to detect a change in the current, and to detect a target load
based on the change in the current. The target load includes a load of
which the output power is applied thereto.

[0009] The controller is further configured to determine the output power.

[0010] The wireless power transmitter further includes a power converter
configured to output the output power.

[0011] The load is applied to an output of the power converter.

[0012] The wireless power transmitter further includes a power supply
configured to apply, to the power converter, a voltage based on a control
of the controller.

[0013] The controller is further configured to determine a state of a
wireless power transmission based on the target load.

[0014] When the current is less than a predetermined value, the controller
is further configured to terminate a charging of the target device.

[0015] The controller is further configured to adjust the output power
based on the target load.

[0016] The target load includes a sum of loads of target devices.

[0017] The current is changed based on a change in a charging mode of the
target device from a constant current (CC) mode to a constant voltage
(CV) mode.

[0018] The power detector includes a first resistor in which the current
flows, and a comparator configured to output, to the controller, voltages
applied to a first terminal and a second terminal of the first resistor.
The controller is further configured to detect the target load based on
the voltages and a resistance value of the first resistor.

[0019] The wireless power transmitter further includes a power converter
configured to output the output power. The power detector further
includes a second resistor including a first terminal and a second
terminal, the first terminal being connected to the first terminal of the
first resistor, and the second terminal being connected to a positive
terminal of the comparator. The power detector further includes a third
resistor including a first terminal and a second terminal, the first
terminal being connected to the second terminal of the first resistor and
an input of the power converter, and the second terminal being connected
to a negative terminal of the comparator.

[0020] In another general aspect, there is provided a method of detecting
a load in a wireless power transmission, including wirelessly
transmitting, to a target device, an output power. The method further
includes detecting a current of the output power. The method further
includes detecting a change in the current. The method further includes
detecting a target load based on the change in the current, the target
load including the load of which the output power is applied thereto.

[0021] The method further includes determining a state of the wireless
power transmission based on the target load.

[0022] The method further includes, when the current is less than a
predetermined value, terminating a charging of the target device.

[0023] The method further includes adjusting the output power based on the
target load.

[0024] The target load further includes a sum of loads of target devices.

[0025] The current is changed based on a change in a charging mode of the
target device from a constant current (CC) mode to a constant voltage
(CV) mode.

[0026] The method further includes matching an impedance and a resonant
frequency of a source device to an impedance and a resonant frequency of
the target device.

[0027] A non-transitory computer-readable storage medium storing a program
includes instructions to cause a computer to implement the method.

[0028] Other features and aspects will be apparent from the following
detailed description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 is a diagram illustrating an example of a wireless power
transmission and charging system.

[0030] FIGS. 2A and 2B are diagrams illustrating examples of a
distribution of a magnetic field in a feeder and a source resonator.

[0031] FIGS. 3A and 3B are diagrams illustrating an example of a wireless
power transmitter.

[0032]FIG. 4A is a diagram illustrating an example of a distribution of a
magnetic field within a source resonator based on feeding of a feeding
unit.

[0033]FIG. 4B is a diagram illustrating examples of equivalent circuits
of a feeding unit and a source resonator.

[0034] FIG. 5 is a diagram illustrating an example of a multi-target
device communication environment.

[0035]FIG. 6 is a diagram illustrating an example of a mode of a wireless
power transmission and charging system of FIG. 5.

[0036] FIG. 7 is a block diagram illustrating an example of a
configuration of a source device of FIG. 5.

[0037]FIG. 8 is a block diagram illustrating an example of a
configuration of a target device of FIG. 5.

[0038] FIG. 9 is a diagram illustrating an example of a fluctuation in a
target load.

[0039]FIG. 10 is a diagram illustrating an example of a configuration of
a power detector in the source device.

[0040] FIG. 11 is a diagram illustrating an example of a change in a
battery load.

[0041] FIG. 12 is a diagram illustrating an example of a fluctuation in a
charging current.

[0042]FIG. 13 is a flowchart illustrating an example of a method of
detecting a load for wireless power transmission and of determining a
state of the wireless power transmission.

[0044] FIGS. 15A through 16B are diagrams illustrating examples of
applications in which a wireless power receiver and a wireless power
transmitter may be mounted.

[0045]FIG. 17 is a diagram illustrating an example of a wireless power
transmitter and a wireless power receiver.

[0046] Throughout the drawings and the detailed description, unless
otherwise described, the same drawing reference numerals will be
understood to refer to the same elements, features, and structures. The
relative size and depiction of these elements may be exaggerated for
clarity, illustration, and convenience.

DETAILED DESCRIPTION

[0047] The following detailed description is provided to assist the reader
in gaining a comprehensive understanding of the methods, apparatuses,
and/or systems described herein. Accordingly, various changes,
modifications, and equivalents of the methods, apparatuses, and/or
systems described herein will be suggested to those of ordinary skill in
the art. The progression of processing steps and/or operations described
is an example; however, the sequence of and/or operations is not limited
to that set forth herein and may be changed as is known in the art, with
the exception of steps and/or operations necessarily occurring in a
certain order. Also, description of well-known functions and
constructions may be omitted for increased clarity and conciseness.

[0048] FIG. 1 illustrates a wireless power transmission and charging
system. The wireless power transmission and charging system includes a
source device 110 and a target device 120.

[0049] The source device 110 includes an alternating current-to-direct
current (AC/DC) converter 111, a power detector 113, a power converter
114, a control and communication (control/communication) unit 115, and a
source resonator 116. The target device 120 includes a target resonator
121, a rectification unit 122, a DC-to-DC (DC/DC) converter 123, a switch
unit 124, a charging unit 125, and a control/communication unit 126.

[0050] The AC/DC converter 111 generates a DC voltage by rectifying an AC
voltage in a band of tens of hertz (Hz) output from a power supply 112.
The AC/DC converter 111 outputs a DC voltage of a predetermined level, or
may adjust an output level of a DC voltage based on the control of the
control/communication unit 115.

[0051] The power detector 113 detects an output current and an output
voltage of the AC/DC converter 111, and transfers, to the
control/communication unit 115, information on the detected current and
the detected voltage. Additionally, the power detector 113 may detect an
input current and an input voltage of the power converter 114.

[0052] The power converter 114 generates a power by converting a DC
voltage of a predetermined level to an AC voltage, using a switching
pulse signal in a band of a few kilohertz (KHz) to tens of megahertz
(MHz). For example, the power converter 114 may convert, to an AC
voltage, a DC voltage supplied to a power amplifier (PA), using a
reference resonant frequency FRef. The power converter 114 may
generate a communication power used for communication, or a charging
power used to charge. The communication power and/or the charging power
may be used in a plurality of target devices, e.g., the target device
120. The communication power may refer to low power of 0.1 milliwatt (mW)
to 1 mW, and the charging power may refer to high power of 1 mW to 200 W
that is consumed in a device load of a target device.

[0053] The term "charging" may refer to supplying power to a unit or
element that is configured to charge power. Additionally, the term
"charging" may refer to supplying power to a unit or element that is
configured to consume power. The units or elements may include, for
example, batteries, displays, sound output circuits, main processors,
and/or various sensors.

[0054] The term "reference resonant frequency" may refer to a resonant
frequency that is used by the source device 110. Additionally, the term
"tracking frequency" may refer to a resonant frequency that is adjusted
by a preset scheme.

[0055] The control/communication unit 115 detects a reflected wave of the
communication power and/or the charging power, and detects mismatching
between the target resonator 121 and the source resonator 116 based on
the detected reflected wave. To detect the mismatching, the
control/communication unit 115 may detect an envelope of the reflected
wave, or detect a power amount of the reflected wave. The
control/communication unit 115 computes a voltage standing wave ratio
(VSWR) based on a voltage level of the reflected wave, and based on a
level of an output voltage of the source resonator 116 or the power
converter 114. For example, when the VSWR is less than a predetermined
value, the control/communication unit 115 determines that the mismatching
is detected. In this example, the control/communication unit 115 computes
a power transmission efficiency for each of N tracking frequencies that
are set in advance, may determine a tracking frequency FBest with
the best power transmission efficiency among the N tracking frequencies,
and may adjust the reference resonant frequency FRef to the tracking
frequency FBest.

[0056] Additionally, the control/communication unit 115 controls a
frequency of a switching pulse signal. Under the control of the
control/communication unit 115, the frequency of the switching pulse
signal is determined. By controlling the power converter 114, the
control/communication unit 115 generates a modulation signal to be
transmitted to the target device 120. In other words, the
control/communication unit 115 may transmit various messages to the
target device 120 using in-band communication. Additionally, the
control/communication unit 115 may detect a reflected wave of the
communication power and/or the charging power, and may demodulate a
signal received from the target device 120 through an envelope of the
detected reflected wave.

[0057] The control/communication unit 115 may generate a modulation signal
for in-band communication, using various methods. For example, to
generate a modulation signal, the control/communication unit 115 may turn
on or off a switching pulse signal, or may perform delta-sigma
modulation. In another example, the control/communication unit 115 may
generate a pulse-width modulation (PWM) signal with a predetermined
envelope.

[0058] The control/communication unit 115 may also perform out-band
communication that employs a communication channel. The
control/communication unit 115 may include a communication module, such
as, for example, a ZigBee module, a Bluetooth module, and/or the like.
The control/communication unit 115 may transmit or receive data to or
from the target device 120 through the out-band communication.

[0059] The source resonator 116 transfers an electromagnetic energy to the
target resonator 121. For example, the source resonator 116 transfers, to
the target device 120, the communication power and/or the charging power,
using a magnetic coupling with the target resonator 121.

[0060] The target resonator 121 receives the electromagnetic energy from
the source resonator 116. For example, the target resonator 121 receives,
from the source device 110, the communication power and/or charging
power, using the magnetic coupling with the source resonator 116.
Additionally, the target resonator 121 may receive various messages from
the source device 110 using the in-band communication.

[0061] The rectification unit 122 generates a DC voltage by rectifying an
AC voltage. The AC voltage is received from the target resonator 121.

[0062] The DC/DC converter 123 adjusts a level of the DC voltage output
from the rectification unit 122 based on a capacitance of the charging
unit 125. For example, the DC/DC converter 123 may adjust the level of
the DC voltage output to 3 volt (V) through 10 V.

[0063] The switch unit 124 is turned on or off under the control of the
control/communication unit 126. When the switch unit 124 is turned off,
the control communication unit 115 of the source device 110 detects a
reflected wave. In other words, when the switch unit 124 is turned off,
the magnetic coupling between the source resonator 116 and the target
resonator 121 is eliminated.

[0064] The charging unit 125 may include a battery. The charging unit 125
may charge the battery using a DC voltage output from the DC/DC converter
123.

[0065] The control/communication unit 126 may perform in-band
communication to transmit or receive data using a resonant frequency.
During the in-band communication, the control/communication unit 126 may
demodulate a received signal by detecting a signal between the target
resonator 121 and the rectification unit 122, or by detecting an output
signal of the rectification unit 122. In other words, the
control/communication unit 126 may demodulate a message received through
the in-band communication.

[0066] Additionally, the control/communication unit 126 adjusts an
impedance of the target resonator 121 to modulate a signal to be
transmitted to the source device 110. For example, the
control/communication unit 126 may modulate the signal to be transmitted
to the source device 110 by turning on or off the switch unit 124. In
this example, the control/communication unit 126 may increase the
impedance of the target resonator 121 so that a reflected wave may be
detected by the control/communication unit 115 of the source device 110.
Depending on whether the reflected wave is detected, the
control/communication unit 115 may detect a binary number "0" or "1".

[0067] The control/communication unit 126 transmits a response message to
the source device 110. The response message may include, for example, a
type of the corresponding target device 120, "information on a
manufacturer of the corresponding target device 120, a model name of the
corresponding target device 120, and/or a battery type of the
corresponding target device 120,. The response message may further
include, for example, a scheme of charging the corresponding target
device 120, an impedance value of a load of the corresponding target
device 120, and/or information on characteristics of the target resonator
121 of the corresponding target device 120. The response message may
further include, for example, information on a frequency band used by the
corresponding target device 120, an amount of a power consumed by the
corresponding target device 120, an identifier (ID) of the corresponding
target device 120, and/or information on a version or standard of the
corresponding target device.

[0068] The control/communication unit 126 may also perform out-band
communication that employs a communication channel. The
control/communication unit 126 may include a communication module, such
as, for example, a ZigBee module, a Bluetooth module, and/or the like.
The control/communication unit 126 may transmit or receive data to or
from the source device 110 through the out-band communication.

[0069] The control/communication unit 126 receives a wake-up request
message from the source device 110, detects an amount of a power received
by the target resonator 121, and transmits, to the source device 110,
information on the detected amount of the power. The information on the
detected amount may include, for example, an input voltage value and an
input current value of the rectification unit 122, an output voltage
value and an output current value of the rectification unit 122, an
output voltage value and an output current value of the DC/DC converter
123, and/or the like.

[0070] The control/communication unit 115 sets a resonance bandwidth of
the source resonator 116. Based on a setting of the resonance bandwidth
of the source resonator 116, a Q-factor of the source resonator 116 may
be determined.

[0071] Additionally, the control/communication unit 126 sets a resonance
bandwidth of the target resonator 121. Based on a setting of the
resonance bandwidth of the target resonator 121, a Q-factor of the target
resonator 121 may be determined.

[0072] The resonance bandwidth of the source resonator 116 may be set to
be wider or narrower than the resonance bandwidth of the target resonator
121. The source device 110 and the target device 120 communicate with
each other to share information on the resonance bandwidth of the source
resonator 116 and the resonance bandwidth of the target resonator 121. In
an example in which power required by the target device 120 is higher
than a reference value, the Q-factor of the source resonator 116 may be
set to a value greater than 100. In another example in which the power
required by the target device 120 is lower than the reference value, the
Q-factor of the source resonator 116 may be set to a value less than 100.

[0073] In a wireless power transmission employing a resonance scheme, the
resonance bandwidth may be an important factor. In an example in which a
Q-factor Qt considers a change in a distance between the source resonator
116 and the target resonator 121, a change in a resonance impedance,
impedance mismatching, a reflected signal, and/or the like, Qt may have
an inverse-proportional relationship with the resonance bandwidth, as
given by Equation 1.

[0074] In Equation 1, f0 denotes a central frequency, Δf
denotes a change in a bandwidth, ΓS.D denotes a reflection
loss between the source resonator 116 and the target resonator 121,
BWS denotes the resonance bandwidth of the source resonator 116, and
BWD denotes the resonance bandwidth of the target resonator 121.

[0075] An efficiency U of the wireless power transmission may be defined,
as given in Equation 2.

[0076] In Equation 2, K denotes a coupling coefficient of energy coupling
between the source resonator 116 and the target resonator 121,
ΓS denotes a reflection coefficient in the source resonator
116, ΓD denotes a reflection coefficient in the target
resonator 121, ω0 denotes a resonant frequency, M denotes a
mutual inductance between the source resonator 116 and the target
resonator 121, RS denotes an impedance of the source resonator 116,
RD denotes an impedance of the target resonator 121, QS denotes
the Q-factor of the source resonator 116, QD denotes the Q-factor of
the target resonator 121, and QK denotes a Q-factor of an energy
coupling between the source resonator 116 and the target resonator 121.

[0077] Referring to Equation 2, the Q-factors may have high relevance to
the efficiency of the wireless power transmission. Accordingly, to
increase the efficiency of the wireless power transmission, the Q-factors
may be set to higher values. However, when the Q-factors QS and
QD are set to higher values, the efficiency of the wireless power
transmission is reduced due to, for example, a change in the coupling
coefficient κ, the change in the distance between the source
resonator 116 and the target resonator 121, the change in the resonance
impedance, impedance mismatching, and/or the like.

[0078] Thus, to increase the efficiency of the wireless power
transmission, when the resonance bandwidth of the source resonator 116
and the resonance bandwidth of the target resonator 121 are set to be
narrower, impedance mismatching and the like occur even due to a small
external effect. Considering the impedance mismatching, Equation 1 may be
represented as given in Equation 3.

Δ f f 0 = VSWR - 1 Qt VSWR [
Equation 3 ] ##EQU00003##

[0079] In an example in which an unbalanced relationship of a resonance
bandwidth, or a bandwidth of an impedance matching frequency between the
source resonator 116 and the target resonator 121, is maintained, the
efficiency of the wireless power transmission may be prevented from being
reduced due to, for example, the change in the coupling coefficient
κ, the change in the distance between the source resonator 116 and
the target resonator 121, the change in the resonance impedance, the
impedance mismatching, and/or the like. When the unbalanced relationship
of the resonance bandwidth, or the bandwidth of the impedance matching
frequency between the source resonator 116 and the target resonator 121,
is maintained, based on Equations 1 and 3, an unbalanced relationship
between the Q-factors QS and QD is also maintained.

[0080] Hereinafter, the term "resonator" in FIGS. 2A through 4B may
include, for example, a source resonator and a target resonator.

[0081] FIGS. 2A and 2B illustrate examples of a distribution of a magnetic
field in a feeder and a resonator. In an example in which a resonator
receives power supply through a separate feeder, magnetic fields are
formed in both the feeder and the resonator.

[0082] Referring to FIG. 2A, as an input current flows in a feeder 210, a
magnetic field 230 is formed. A direction 231 of the magnetic field 230
within the feeder 210 has a phase opposite to a phase of a direction 233
of the magnetic field 230 outside the feeder 210. The magnetic field 230
causes an induced current to be formed in a source resonator 220. Here, a
direction of the induced current is opposite to a direction of the input
current.

[0083] Due to the induced current, a magnetic field 240 is formed in the
source resonator 220. Directions of a magnetic field formed due to an
induced current in all positions of the source resonator 220 are
identical. Accordingly, a direction 241 of the magnetic field 240 formed
by the source resonator 220 has the same phase as a direction 243 of the
magnetic field 240 formed by the source resonator 220.

[0084] Consequently, when the magnetic field 230 formed by the feeder 210
and the magnetic field 240 formed by the source resonator 220 are
combined, strength of a total magnetic field decreases within the feeder
210, but increases outside the feeder 210. In an example in which a power
is supplied to the source resonator 220 through the feeder 210, the
strength of the total magnetic field decreases in the center of the
source resonator 220, but increases in outer edges of the source
resonator 220. When a magnetic field is randomly distributed in the
source resonator 220, it may be difficult to perform impedance matching
since an input impedance may frequently vary. Additionally, when the
strength of the total magnetic field is increased, an efficiency of
wireless power transmission is increased. Conversely, when the strength
of the total magnetic field is decreased, the efficiency for wireless
power transmission is reduced. Accordingly, a power transmission
efficiency is reduced on average.

[0085] As an example, in a target resonator, a magnetic field may be
distributed as illustrated in FIG. 2A. For example, a current flowing in
the source resonator 220 is induced by the input current flowing in the
feeder 210. A current flowing in the target resonator is induced by a
magnetic coupling between the source resonator 220 and the target
resonator. The current flowing in the target resonator cases a magnetic
field to be formed so that an induced current is generated in a feeder
located in the target resonator. In this example, within the feeder, a
direction of a magnetic field formed by the target resonator has a phase
opposite to a phase of a direction of a magnetic field formed by the
feeder and accordingly, strength of a total magnetic field is reduced.

[0086]FIG. 2B illustrates a structure of a wireless power transmitter in
which a source resonator 250 and a feeder 260 have a common ground. The
source resonator 250 includes a capacitor 251. The feeder 260 receives an
input of a radio frequency (RF) signal via a port 261.

[0087] For example, when the RF signal is received to the feeder 260, an
input current is generated in the feeder 260. The input current flowing
in the feeder 260 causes a magnetic field to be formed, and a current is
induced in the source resonator 250 by the magnetic field. Additionally,
another magnetic field is formed due to the induced current flowing in
the source resonator 250. In this example, a direction of the input
current flowing in the feeder 260 has a phase opposite to a phase of a
direction of the induced current flowing in the source resonator 250.
Accordingly, in a region between the source resonator 250 and the feeder
260, a direction 271 of the magnetic field formed due to the input
current has the same phase as a direction 273 of the magnetic field
formed due to the induced current, and thus the strength of a total
magnetic field increases. Conversely, within the feeder 260, a direction
281 of the magnetic field formed due to the input current has a phase
opposite to a phase of a direction 283 of the magnetic field formed due
to the induced current, and thus the strength of the total magnetic field
decreases. Therefore, the strength of the total magnetic field decreases
in the center of the source resonator 250, but increases in outer edges
of the source resonator 250.

[0088] The feeder 260 determines an input impedance by adjusting an
internal area of the feeder 260. The input impedance refers to an
impedance viewed in a direction from the feeder 260 to the source
resonator 250. When the internal area of the feeder 260 is increased, the
input impedance is increased. Conversely, when the internal area of the
feeder 260 is reduced, the input impedance is reduced. Since the magnetic
field is randomly distributed in the source resonator 250 despite a
reduction in the input impedance, a value of the input impedance varies
depending on a location of a target device.

[0089] Accordingly, a separate matching network is required to match the
input impedance to an output impedance of a PA. For example, when the
input impedance is increased, a separate matching network is used to
match the increased input impedance to a relatively low output impedance.
As an example, when a target resonator has the same configuration as the
source resonator 250, and when a feeder of the target resonator has the
same configuration as the feeder 260, a separate matching network is
required, because a direction of a current flowing in the target
resonator has a phase opposite to a phase of a direction of an induced
current flowing in the feeder of the target resonator.

[0090]FIG. 3A illustrates an example of a wireless power transmitter. The
wireless power transmitter includes a resonator 310 and a feeding unit
320. The resonator 310 includes a capacitor 311. The feeding unit 320 may
be electrically connected to both ends of the capacitor 311.

[0091] FIG. 3B illustrates, in detail, an example of a structure of the
wireless power transmitter of FIG. 3A. The resonator 310 includes a first
transmission line, a first conductor 341, a second conductor 342, and at
least one first capacitor 350.

[0092] The first capacitor 350 is inserted in series between a first
signal conducting portion 331 and a second signal conducting portion 332
in the first transmission line, and an electric field is confined within
the first capacitor 350. For example, the first transmission line
includes at least one conductor in an upper portion of the first
transmission line, and includes at least one conductor in a lower portion
of the first transmission line. Current flows through the at least one
conductor disposed in the upper portion of the first transmission line,
and the at least one conductor disposed in the lower portion of the first
transmission line is electrically grounded. For example, a conductor
disposed in an upper portion of the first transmission line is separated
into and thereby referred to as the first signal conducting portion 331
and the second signal conducting portion 332. A conductor disposed in a
lower portion of the first transmission line is referred to as a first
ground conducting portion 333.

[0093] As illustrated in FIG. 3B, the resonator 310 has a two-dimensional
(2D) structure. The first transmission line includes the first signal
conducting portion 331 and the second signal conducting portion 332 in
the upper portion of the first transmission line. In addition, the first
transmission line includes the first ground conducting portion 333 in the
lower portion of the first transmission line. The first signal conducting
portion 331 and the second signal conducting portion 332 are disposed to
face the first ground conducting portion 333. The current flows through
the first signal conducting portion 331 and the second signal conducting
portion 332.

[0094] Additionally, one end of the first signal conducting portion 331 is
shorted to the first conductor 341, and another end of the first signal
conducting portion 331 is connected to the first capacitor 350. One end
of the second signal conducting portion 332 is shorted to the second
conductor 342, and another end of the second signal conducting portion
332 is connected to the first capacitor 350. Accordingly, the first
signal conducting portion 331, the second signal conducting portion 332,
the first ground conducting portion 333, and the conductors 341 and 342
are connected to each other, so that the resonator 310 has an
electrically closed-loop structure. The term "loop structure" may
include, for example, a polygonal structure such as a circular structure,
a rectangular structure, and/or the like. "Having a loop structure" may
indicate that the circuit is electrically closed.

[0095] The first capacitor 350 is inserted into an intermediate portion of
the first transmission line. For example, the first capacitor 350 is
inserted into a space between the first signal conducting portion 331 and
the second signal conducting portion 332. The first capacitor 350 may
have a shape of, for example, a lumped element, a distributed element,
and/or the like. For example, a distributed capacitor having the shape of
the distributed element may include zigzagged conductor lines and a
dielectric material that has a high permittivity between the zigzagged
conductor lines.

[0096] When the first capacitor 350 is inserted into the first
transmission line, the resonator 310 has a characteristic of a
metamaterial. The metamaterial indicates a material having a
predetermined electrical property that has not been discovered in nature,
and thus, has an artificially designed structure. An electromagnetic
characteristic of the materials existing in nature may have a unique
magnetic permeability or a unique permittivity. Most materials may have a
positive magnetic permeability or a positive permittivity.

[0097] In the case of most materials, a right hand rule may be applied to
an electric field, a magnetic field, and a pointing vector, and thus, the
corresponding materials may be referred to as right handed materials
(RHMs). However, the metamaterial that has a magnetic permeability or a
permittivity absent in nature may be classified into, for example, an
epsilon negative (ENG) material, a mu negative (MNG) material, a double
negative (DNG) material, a negative refractive index (NRI) material, a
left-handed (LH) material, and/or the like, based on a sign of the
corresponding permittivity or magnetic permeability.

[0098] When a capacitance of the first capacitor 350 inserted as the
lumped element is appropriately determined, the resonator 310 has the
characteristic of the metamaterial. Because the resonator 310 may have a
negative magnetic permeability by appropriately adjusting the capacitance
of the first capacitor 350, the resonator 310 may also be referred to as
an MNG resonator. Various criteria may be applied to determine the
capacitance of the first capacitor 350. For example, the various criteria
may include, for example, a criterion that enables the resonator 310 to
have the characteristic of the metamaterial, a criterion that enables the
resonator 310 to have a negative magnetic permeability in a target
frequency, a criterion that enables the resonator 310 to have a zeroth
order resonance characteristic in the target frequency, and/or the like.
Based on at least one criterion among the aforementioned criteria, the
capacitance of the first capacitor 350 is determined.

[0099] The resonator 310, also referred to as the MNG resonator 310, may
have a zeroth order resonance characteristic of having, as a resonant
frequency, a frequency when a propagation constant is 0. Because the
resonator 310 may have the zeroth order resonance characteristic, the
resonant frequency may be independent with respect to a physical size of
the MNG resonator 310. By appropriately designing the first capacitor
350, the MNG resonator 310 may sufficiently change the resonant
frequency. Accordingly, the physical size of the MNG resonator 310 may
not be changed.

[0100] In a near field, the electric field is concentrated on the first
capacitor 350 inserted into the first transmission line. Accordingly, due
to the first capacitor 350, the magnetic field becomes dominant in the
near field. The MNG resonator 310 may have a relatively high Q-factor
using the first capacitor 350 of the lumped element, and thus, it is
possible to enhance an efficiency of power transmission. For example, the
Q-factor may indicate a level of an ohmic loss or a ratio of a reactance
with respect to a resistor in the wireless power transmission. The
efficiency of the wireless power transmission may increase according to
an increase in the Q-factor.

[0101] Although not illustrated in FIG. 3B, a magnetic core may be further
provided to pass through the MNG resonator 310. The magnetic core may
perform a function of increasing a power transmission distance.

[0102] Referring to FIG. 3B, the feeding unit 320 includes a second
transmission line, a third conductor 371, a fourth conductor 372, a fifth
conductor 381, and a sixth conductor 382. The second transmission line
includes a third signal conducting portion 361 and a fourth signal
conducting portion 362 in an upper portion of the second transmission
line. In addition, the second transmission line includes a second ground
conducting portion 363 in a lower portion of the second transmission
line. The third signal conducting portion 361 and the fourth signal
conducting portion 362 are disposed to face the second ground conducting
portion 363. Current flows through the third signal conducting portion
361 and the fourth signal conducting portion 362.

[0103] Additionally, one end of the third signal conducting portion 361 is
shorted to the third conductor 371, and another end of the third signal
conducting portion 361 is connected to the fifth conductor 381. One end
of the fourth signal conducting portion 362 is shorted to the fourth
conductor 372, and another end of the fourth signal conducting portion
362 is connected to the sixth conductor 382. The fifth conductor 381 is
connected to the first signal conducting portion 331, and the sixth
conductor 382 is connected to the second signal conducting portion 332.
The fifth conductor 381 and the sixth conductor 382 are connected in
parallel to both ends of the first capacitor 350. Here, the fifth
conductor 381 and the sixth conductor 382 are used as input ports to
receive an input of an RF signal.

[0104] Accordingly, the third signal conducting portion 361, the fourth
signal conducting portion 362, the second ground conducting portion 363,
the third conductor 371, the fourth conductor 372, the fifth conductor
381, the sixth conductor 382, and the resonator 310 are connected to each
other, so that the resonator 310 and the feeding unit 320 have an
electrically closed-loop structure. The term "loop structure" may
include, for example, a polygonal structure such as a circular structure,
a rectangular structure, and/or the like. When an RF signal is received
via the fifth conductor 381 or the sixth conductor 382, an input current
flows in the feeding unit 320 and the resonator 310, a magnetic field is
formed due to the input current, and a current is induced to the
resonator 310 by the formed magnetic field. A direction of the input
current flowing in the feeding unit 320 is identical to a direction of
the induced current flowing in the resonator 310 and thus, strength of a
total magnetic field increases in the center of the resonator 310, but
decreases in outer edges of the resonator 310.

[0105] An input impedance is determined based on an area of a region
between the resonator 310 and the feeding unit 320 and accordingly, a
separate matching network used to match the input impedance to an output
impedance of a power amplifier is not be required. For example, even when
the matching network is used, the input impedance is determined by
adjusting a size of the feeding unit 320 and thus, a structure of the
matching network is simplified. The simplified structure of the matching
network minimizes a matching loss of the matching network.

[0106] The second transmission line, the third conductor 371, the fourth
conductor 372, the fifth conductor 381, and the sixth conductor 382 form
the same structure as the resonator 310. In an example in which the
resonator 310 has a loop structure, the feeding unit 320 may also have a
loop structure. In another example in which the resonator 310 has a
circular structure, the feeding unit 320 may also have a circular
structure.

[0107]FIG. 4A illustrates an example of a distribution of a magnetic
field within a resonator based on feeding of a feeding unit. For example,
FIG. 4A more briefly illustrates the resonator 310 and the feeding unit
320 of FIG. 3A. FIG. 4B illustrates an example of an equivalent circuit
of a feeding unit 440, and an equivalent circuit of a resonator 450.

[0108] A feeding operation in a wireless power transmission may refer to
supplying a power to a source resonator, or may refer to supplying an AC
power to a rectification unit. FIG. 4A illustrates a direction of an
input current flowing in the feeding unit, and a direction of an induced
current induced in the source resonator. Additionally, FIG. 4A
illustrates a direction of a magnetic field formed due to the input
current of the feeding unit, and a direction of a magnetic field formed
due to the induced current of the source resonator.

[0109] Referring to FIG. 4A, a fifth conductor or a sixth conductor of the
feeding unit may be used as an input port 410. The input port 410
receives an input of an RF signal. The RF signal may be output from a PA.
The PA may increase or decrease an amplitude of the RF signal on demand
by a target device. The RF signal received by the input port 410 is shown
in the form of an input current flowing in the feeding unit. The input
current flows in a clockwise direction in the feeding unit, along a
transmission line of the feeding unit. The fifth conductor of the feeding
unit is electrically connected to the resonator. For example, the fifth
conductor may be connected to a first signal conducting portion of the
resonator. Accordingly, the input current flows in the resonator, as well
as, in the feeding unit. The input current flows in a counterclockwise
direction in the resonator. The input current flowing in the resonator
causes a magnetic field to be formed so that an induced current is
generated in the resonator due to the magnetic field. The induced current
flows in a clockwise direction in the resonator. Here, the induced
current transfers energy to a capacitor of the resonator, and a magnetic
field is formed due to the induced current. The input current flowing in
the feeding unit and the resonator is indicated by a solid line of FIG.
4A, and the induced current flowing in the resonator is indicated by a
dotted line of FIG. 4A.

[0110] A direction of a magnetic field formed due to a current is
determined based on the right hand rule. As illustrated in FIG. 4A,
within the feeding unit, a direction 421 of a magnetic field formed due
to the input current flowing in the feeding unit is identical to a
direction 423 of a magnetic field formed due to the induced current
flowing in the resonator. Accordingly, strength of a total magnetic field
increases within the feeding unit.

[0111] Additionally, in a region between the feeding unit and the
resonator, a direction 433 of a magnetic field formed due to the input
current flowing in the feeding unit has a phase opposite to a phase of a
direction 431 of a magnetic field formed due to the induced current
flowing in the resonator, as illustrated in FIG. 4A. Accordingly,
strength of the total magnetic field decreases in the region between the
feeding unit and the resonator.

[0112] Typically, a strength of a magnetic field decreases in the center
of a resonator with the loop structure, and increases in outer edges of
the resonator. However, referring to FIG. 4A, the feeding unit is
electrically connected to both ends of a capacitor of the resonator, and
accordingly the induced current of the resonator flows in the same
direction as the input current of the feeding unit. Since the induced
current of the resonator flows in the same direction as the input current
of the feeding unit, the strength of the total magnetic field increases
within the feeding unit, and decreases outside the feeding unit. As a
result, the strength of the total magnetic field increases in the center
of the resonator with the loop structure, and decreases in the outer
edges of the resonator, due to the feeding unit. Thus, the strength of
the total magnetic field is equalized within the resonator.

[0113] Additionally, a power transmission efficiency of transferring a
power from a source resonator to a target resonator is in proportion to
the strength of the total magnetic field formed in the source resonator.
In other words, when the strength of the total magnetic field increases
in the center of the source resonator, the power transmission efficiency
also increases.

[0114] Referring to FIG. 4B, the feeding unit 440 and the resonator 450
may be expressed by the equivalent circuits. An input impedance Zin
viewed in a direction from the feeding unit 440 to the resonator 450 may
be computed, as given in Equation 4.

Z i n = ( ω M ) 2 Z [ Equation
4 ] ##EQU00004##

[0115] In Equation 4, M denotes a mutual inductance between the feeding
unit 440 and the resonator 450, ω denotes a resonant frequency
between the feeding unit 440 and the resonator 450, and Z denotes an
impedance viewed in a direction from the resonator 450 to a target
device. The input impedance Zin may be in proportion to the mutual
inductance M. Accordingly, the input impedance Zin may be controlled
by adjusting the mutual inductance M. The mutual inductance M may be
adjusted based on an area of a region between the feeding unit 440 and
the resonator 450. The area of the region between the feeding unit 440
and the resonator 450 may be adjusted based on a size of the feeding unit
440. In other words, the input impedance Zin may be determined based
on the size of the feeding unit 440, and thus a separate matching network
may not be required to perform impedance matching with an output
impedance of a PA.

[0116] In a target resonator and a feeding unit included in a wireless
power receiver, a magnetic field may be distributed as illustrated in
FIG. 4A. For example, the target resonator may receive a wireless power
from a source resonator, using magnetic coupling. Due to the received
wireless power, an induced current may be generated in the target
resonator. A magnetic field formed due to the induced current in the
target resonator may cause another induced current to be generated in the
feeding unit. In this example, when the target resonator is connected to
the feeding unit as illustrated in FIG. 4A, the induced current generated
in the target resonator may flow in the same direction as the induced
current generated in'the feeding unit. Thus, strength of a total magnetic
field may increase within the feeding unit, but may decrease in a region
between the feeding unit and the target resonator.

[0117] FIG. 5 illustrates an example of a multi-target device
communication environment. A wireless power transmission and charging
system 500 includes a single source device 510 and at least one target
device 520. The source device 510 and the target device 520 may be, for
example, the source device 110 and the target device 120 of FIG. 1,
respectively.

[0118] The source device 510 transmits power to the at least one target
device 520. The source device 510 also outputs an anti-collision data
command. The at least one target device 520 respectively includes at
least one battery.

[0119] In an example, a plurality of target devices, including the target
device 520, may simultaneously approach a resonator of the source device
510, or may exist within a range of the resonator of the source device
510. When a power is supplied to the source device 510, data collision
may occur during an operation for initial connection between the
plurality of target devices and the source device 510. Due to the data
collision, a normal charging operation may not be performed.

[0120]FIG. 6 illustrates an example of a mode of the wireless power
transmission and charging system 500 of FIG. 5. The wireless power
transmission and charging system 500 may be operated in three modes, in
terms of software. The three modes may include, for example, a standby
mode, a connection mode, and a transmission and charging control mode.

[0121] The standby mode includes a state in which no target device 520
exists within a power transmission distance of the source device 510. The
connection mode includes a mode in which the source device 510 verifies
information on a type and a serial number of the target device 520, and
on an amount of power used by the target device 520, through an initial
connection between the source device 510 and the target device 520. The
source device 510 controls the target device 520 to enter the
transmission and charging control mode. The initial connection may be
performed when the target device 520 exists within the power transmission
distance of the source device 510.

[0122] In the connection mode, a plurality of target devices, including
the target device 520, may simultaneously send a connection request
(e.g., data) to the single source device 510. Hereinafter, a method of
processing one-to-one communication to be performed between the source
device 510 and each of the target devices when the target devices
simultaneously send a connection request to the source device 510, will
be further described.

[0123] The transmission and charging control mode includes a state in
which the source device 510 communicates with the target device 520
through a slot assigned by the source device 510 to the target device 520
in the connection mode, and in which the source device 510 transmits
energy or power to charge the target device 520. In terms of the source
device 510, an overall operation of the wireless power transmission and
charging system 500 is classified. For example, in the single target
device 520, the standby mode, the connection mode, and the transmission
and charging control mode, may be sequentially repeated. In another
example, the single source device 510 and N target devices, including the
target device 520, may perform complex and repetitive operations. For
example, when a portion of the plurality of target devices (e.g., the
target device 520) is in the charging mode, another portion of the target
devices may be completely charged already, and a new target device may
try to perform the connection mode with the source device 510.

[0124] FIG. 7 illustrates an example of a configuration of the source
device 510. The source device 510 includes a control/communication unit
710, a power supply 720, a power detector 730, an oscillator 740, a PA
750, a matching controller 755, and a source resonator 760 (namely, a
transmission (Tx) resonator).

[0125] The control/communication unit 710 may be, for example, the
control/communication unit 115 of FIG. 1. The power supply 720 may be,
for example, the power supply 112 and the AC/DC converter 111 of FIG. 1.
Additionally, the power detector 730 may be, for example, the power
detector 113 of FIG. 1. The PA 750 may be, for example, the power
converter 114 of FIG. 1, and the source resonator 760 may be, for
example, the source resonator 116 of FIG. 1. The control/communication
unit 710 may include a power supply controller 712, or the source device
510 may further include the power supply controller 712.

[0126] The oscillator 740 generates a signal with a frequency in a band of
a few KHz to tens of MHz. The generated signal may be the switching pulse
signal of FIG. 1. The signal generated by the oscillator 740 is applied
to the PA 750. The oscillator 740 may change the frequency of the signal,
and a matching schematic. The control/communication unit 710 may control
the oscillator 740 to change the frequency of the generated signal and
the matching schematic.

[0127] The power supply 720 may be, for example, a switching mode power
supply. The power supply controller 712 controls the power supply 720.
For example, the power supply controller 712 controls the power supply
720 to apply a supply power to the PA 750. The power applied to the PA
750 by the power supply 720 may be referred to as a "PA supply power."
Additionally, the power supply controller 712 may control the power
supply 720 to adjust a voltage applied to the PA 750. The voltage applied
to the PA 750 by the power supply 720 may be referred to as a "PA supply
voltage." When the power supply 720 adjusts the PA supply voltage,
current supplied to the PA 750 is also adjusted.

[0128] The PA 750 may be, for example, a variable switching amplifier. The
PA 750 may be designed as a switching amplifier of an E-class. A power
output by the PA 750 is determined based on a frequency of a signal
applied from the oscillator 740, and the supply power applied from the
power supply 720. The power output by the PA 750 may be referred to as a
"PA power". Additionally, a PA current may refer to a current supplied to
the PA 750 when the power supply controller 712 controls the power supply
720. A PA voltage may refer to a voltage of the PA power.

[0129] The source resonator 760 transmits, to a target device (e.g., the
target device 520 in FIG. 6), the PA power as an electromagnetic energy.
The matching controller 755 may be, for example, a matching circuit. The
matching controller 755 changes a matching impedance and a matching
frequency. The control/communication unit 710 controls the matching
controller 755 to change a matching impedance and a matching frequency.

[0130] The power detector 730 detects a current and voltage of the supply
power output by the power supply 720, and transmits, to the
control/communication unit 710, information on the detected current and
the detected voltage. For example, the power detector 730 detects either
the PA power, or the PA current and the PA voltage, and transmits, to the
control/communication unit 710, information on either the detected PA
power, or the detected PA current and the detected PA voltage.
Additionally, the power detector 730 monitors power supply to the target
device by detecting a change in a load and a change in a mode of the
target device. The power detector 730 uses the detected change in the
load and the detected change in the mode to demodulate a modulated load
of the target device.

[0131]FIG. 8 illustrates an example of a configuration of the target
device 520. The target device 520 includes a target resonator 810, a
matching controller 815, a rectification unit 820, a modulation and
demodulation (modulation/demodulation) unit 830, a DC/DC converter 840, a
power detector 860, a control/communication unit 870, a switch unit 880,
and a load 890. The target resonator 810, the rectification unit 820, the
DC/DC converter 840, the control/communication unit 870, the switch unit
880, and the load 890 may be, for example, the target resonator 121, the
rectification unit 122, the DC/DC converter 123, the
control/communication unit 126, the switch unit 124, and the charging
unit 125 of FIG. 1, respectively.

[0132] The target resonator 810 receives an electromagnetic energy from a
source resonator of a source device, e.g., the source resonator 760 of
the source device 510 in FIG. 7. For example, the target resonator 810
receives a power from the source device through a magnetic coupling with
the source resonator. The received power may be used as a communication
power or charging power. Additionally, the target resonator 810 may
receive various messages from the source device through in-band
communication.

[0133] The matching controller 815 performs impedance matching between the
target resonator 810 and the rectification unit 820. The matching
controller 815 may be, for example, a matching circuit. The matching
controller 815 may change a matching impedance and a matching frequency.
The control/communication unit 870 may control the matching controller
815 to change a matching impedance and a matching frequency.

[0134] The rectification unit 820 generates a DC voltage by rectifying an
AC voltage output from the target resonator 810. In other words, the
rectification unit 820 rectifies the AC voltage received via the target
resonator 810.

[0135] The DC/DC converter 840 adjusts a level of the DC voltage output
from the rectification unit 820 based on a capacitance of the load 890.
For example, the DC/DC converter 840 may adjust the level of the DC
voltage to 3 V through 10 V.

[0136] The power detector 860 detects an output power and an output
voltage of the DC/DC converter 840. The power detector 860 transfers, to
the control/communication unit 870, the detected output power and the
detected output voltage.

[0137] The switch unit 880 is turned on or off under the control of the
control/communication unit 870. For example, when the target device 520
or the load 890 is completely charged, the switch unit 880 is turned off.
When the switch unit 880 is turned off, the control/communication unit
(e.g., the control/communication unit 710 in FIG. 7) of the source device
detects a power received by the target device 520. In other words, when
the switch unit 880 is turned off, a magnetic coupling between the source
resonator and the target resonator 810 is eliminated.

[0138] The load 890 may include a battery. The load 890 may include the
charging unit 125 of FIG. 1. The load 890 is charged using a DC voltage
output from the DC/DC converter 840.

[0139] The control/communication unit 870 may perform in-band
communication with the source device using a resonant frequency. To
perform the in-band communication, the control/communication unit 870 may
use the modulation/demodulation unit 830. For example, the
control/communication unit 870 may include the modulation/demodulation
unit 830, and a function of the modulation/demodulation unit 830 may be
performed by the control/communication unit 870.

[0140] The modulation/demodulation unit 830 may detect a signal
transmitted between the target resonator 810 and the rectification unit
820, or may detect an output signal of the rectification unit 820. The
modulation/demodulation unit 830 demodulates a signal received by the
target device 520. For example, the modulation/demodulation unit 830 may
demodulate the signal received by the target device 520 through the
in-band communication. Additionally, the modulation/demodulation unit 830
demodulates a signal to be transmitted to the source device by adjusting
an impedance of the target resonator 810, or by turning on or off the
switch unit 880.

[0141] FIG. 9 illustrates an example of a fluctuation in a target load.
Two target devices 910 and 920 are illustrated. Types of controlling of a
wirelessly transmitted power may include, for example, controlling an
initial power, controlling a power based on a change in a target load,
controlling a power based on a change from a constant current (CC) mode
to a constant voltage (CV) mode, and/or the like.

[0142] The controlling of the initial power may refer to controlling and
transmitting a wirelessly transmitted power when the source device 510
and the target device 910 or 920 start a connection. In a wireless power
transmission system, the source resonator 760 and the target resonator
810 may differ from each other in efficiency according to manufacturers
or products. Accordingly, power needs to be transmitted by controlling
the initial power based on an efficiency difference between the source
resonator 760 and target resonator 810, and thus, a required power of the
target device 910 or 920 may be appropriately transmitted.

[0143] Additionally, when a number of currently charged target devices 910
and 920 is changed, or a battery charging mode of the target device 910
or 920 is changed, a target load (e.g., total load) is changed. The
battery charging mode may be changed, for example, from the CC mode to
the CV mode.

[0144] The target load may refer to a load measured in an output end of a
PA (e.g., the PA 750 in FIG. 7), that is, a load of a target device
connected to the output end of the PA. The target load may be changed due
to a change in a number of the target devices 910 and 920 that are being
charged through the source device 510, or a change in the battery
charging mode of the target device 910 or 920.

[0145] For example, when the target load is changed, power matched to a
load (e.g., the load 890) changed by the controlling of the power based
on the change in the target load, needs to be transmitted. The
controlling of the power based on the change in the target load may refer
to controlling and transmitting the power based on the changed load,
e.g., the load 890.

[0146] To detect a change in the target load, in the PA, first, current of
the PA, namely, a PA current is detected. Second, a change in the target
load is detected based on a change in the detected PA current. When the
PA current is increased during charging, it is determined that a load
(e.g., the load 890) is added to the target load.

[0147] In more detail, in a charging state, the source device 510
recognizes the target device 910 or 920, and supplies a required power to
the target device 910 or 920. The control/communication unit (e.g., the
control/communication unit 710 in FIG. 7) or the power supply controller
(e.g., the power supply controller 712) may control the power supply
(e.g., the power suppy 720) to provide the PA (e.g., the PA 750) with a
controlled PA supply power. The control/communication unit verifies a PA
current and a charging state via communication. For example, the power
detector (e.g., the power detector 730) detects the change in the PA
current. When the PA current is increased above a reference current
value, the control/communication unit determines that the load 890 is
added to the target load. That is, the control/communication unit
recognizes the added load 890, and controls the PA power accordingly.

[0148] When the PA current is reduced during charging, it is determined
that the target load is reduced, e.g., the load 890 is removed from the
target load. In an example in which the source device 510 is in the
charging state, when a PA current detected by the power detector is
reduced below a current value detected during charging, the
control/communication unit determines that the target load is changed,
e.g., the load 890 is removed from the target load. The
control/communication unit verifies a state of the target device 910 or
920, and controls the PA supply power accordingly.

[0149] When charging is started or is already performed, and when the PA
current is equal to or less than a reference current, it is determined
that there is no target device 910 or 920 to be charged or within a
distance of the source device 510. When there is no target device 910 or
920, only the source resonator 760 is regarded as a load of the PA. For
example, the control/communication unit determines whether the target
device 910 or 920 is to be charged or is within a distance of the source
device 510, according to an output of the PA (for example, the PA
current) compared to a PA current when there is no load.

[0150] In order for the source device 510 to control power and detect a
target load or total load, several conditions need to be satisfied. For
example, to supply a power required by the target device 910 or 920 based
on a change in the load 890, the PA needs to output a power matched to
the target load. To output the power matched to the target load, the
following two conditions need to be satisfied.

[0151] First, an impedance matching condition needs to be satisfied. An
impedance in a source side needs to satisfy a matching condition for a
load impedance. The impedance in the source side may include, for
example, an impedance of the source device 510 including the source
resonator 760, and an impedance of the target resonator 810.

[0152] A value of a reflection coefficient is used to determine whether
the matching condition is satisfied. The reflection coefficient may be
computed by Equation 5.

[0154] Second, a resonant frequency condition between the source device
510 and the target device 910 or 920 needs to be satisfied. The source
device 510 and the target device 910 or 920 need to have the same
resonant frequency.

[0155] The control/communication unit detects a change in the load 890 of
the target device 910 or 920 by detecting the PA supply power supplied by
the power supply. When the impedance of the source resonator 760 is
matched with the impedance of the target resonator 810, the load measured
in the output end of the PA is a sum of at least one load 890 of at least
one target device 910 or 920. For example, when the load 890 of the
target device 910 corresponds to 3 W and the load 890 of the target
device 920 corresponds to 3 W, a total load measured in the output end of
the PA of the source device 510 is 6 W.

[0156] The power output by the PA, namely the PA power, may be determined
based on a change in an output load, as given in Equation 6.

[0158] When the output load R decreases, the output power Pwr may
increase. When the output load R increases, the output power Pwr may
decrease. Based on this, a change in an output or target load may be
detected in wirelessly charging. Detecting a change in the target load
based on the change in the PA current may be used to control the PA power
and to determine whether to communicate with the target device 910 or
920.

[0159]FIG. 10 illustrates an example of a configuration of the power
detector 730 in the source device 510 of FIGS. 5-7 and 9. Referring to
FIG. 10, the power detector730 detects a PA current and transmits the
detected PA current to the control/communication unit 710.

[0160] The AC/DC power source 1010 functions as, e.g., the power supply
720 of FIG. 7. The control/communication unit 710 receives, from the
AC/DC power source 1010, power Vcc that is required to operate the
control/communication unit 710. The control/communication unit 710
controls the AC/DC power source 1010 to adjust a PA supply power that is
output by the AC/DC power source 1010 to the power supply 720. The
control/communication unit 710 controls the oscillator 740 to change a
frequency of a signal generated by the oscillator 740, and a matching
schematic.

[0161] The power detector 730 includes a comparator 1020 and a first
resistor 1060. The power detector 730 further includes a second resistor
1030, a third resistor 1040, and a current detector 1050.

[0162] A first terminal of the first resistor 1060, an output of the AC/DC
power source 1010, and a positive terminal of the comparator 1020 are
connected to each other. Additionally, a second terminal of the first
resistor 1060, an input of the PA 750, and a negative terminal of the
comparator 1020 are connected to each other. The PA current flows to the
first resistor 1060.

[0163] The comparator 1020 controls voltages applied to both the positive
terminal and the negative terminal, and outputs the voltages to the
control/communication unit 710. The voltages applied to both the positive
terminal and the negative terminal of the comparator 1020 are equal to
voltages applied to both the first terminal and the second terminal of
the first resistor 1060. The control/communication unit 710 verifies a
first resistance of the first resistor 1060. Accordingly, the
control/communication unit 710 computes a current Is, namely the PA
current, flowing in the first resistor 1060 based on a resistance value
Rs of the first resistor 1060 and the voltages applied to both the
positive terminal and the negative terminal of the comparator 1020.
Additionally, the control/communication unit 710 detects a target load
based on the computed PA current.

[0164] The second resistor 1030 includes a first terminal and a second
terminal. The first terminal of the second resistor 1030 is connected to
the first terminal of the first resistor 1060. The second terminal of the
second resistor 1030 is connected to the positive terminal of the
comparator 1020. The third resistor 1040 includes a first terminal and a
second terminal. The first terminal of the third resistor 1040 is
connected to the second terminal of the first resistor 1060. The second
terminal of the third resistor 1040 is connected to the negative terminal
of the comparator 1020. The second resistor 1030 and the third resistor
1040 adjust the voltages applied to both the positive terminal and the
negative terminal of the comparator 1020.

[0165] FIG. 11 illustrates an example of a change in a battery load. In a
graph 1100, an x-axis represents time, and a y-axis represents current
and/or voltage. Additionally, in the graph 1100, a solid line indicates
voltage and/or cell, and a dotted line indicates a charging current.

[0166] Prior to charging, the control/communication unit (e.g., 870 in
FIG. 8) verifies a voltage or a temperature of a battery, namely the load
(e.g., 890). The battery is charged through three operations.

[0167] In operation 1110, the battery is charged with a CC. For example,
in operation 1110, a maximum charging current is applied to the battery
until a charging voltage cell voltage limit is reached.

[0168] In operation 1110, for example, a charging current of about 0.5 C
to 0.7 C with respect to a battery capacitance may be applied. Here, C
denotes the capacitance of the battery. For example, when a battery has a
capacitance of 1000 mA, a charging current of about 500 mA to 700 mA is
applied to the battery, to charge the battery. The charging /voltage may
be gradually increased to a range of 4.15 V to 4.2 V.

[0169] Operation 1110 may be divided into, for example, a preliminary
charging operation and a quick charging operation. In the preliminary
charging operation, a charging voltage equal to or less than 3 V may be
applied. In the quick charging operation, a charging voltage equal to or
greater than 3 V may be applied.

[0170] In operation 1120, the battery is charged with a CV. When a
charging voltage reaches a maximum cell voltage, as a charging state of
the battery comes close to a fully charged state, the charging current
starts to drop. In operation 1120, a CV ranging from 4.15 V to 4.2 V may
be maintained as a charging voltage. The charging voltage may be computed
based on. Equation 7.

[0171] In Equation 7, the resistance corresponds to a sum of a battery
internal resistance and a circuit resistance. As illustrated in Equation
7, as the resistance increases, a voltage charging time may be
lengthened.

[0172] In a point 1140 at which the charging current is reduced below 3%
of a rated current, operation 1120 may be terminated. For example, when
the charging current becomes lower than a reference value, for example 3%
of the rated current, due to an increase in a charge amount in the
battery, the control/communication unit detects a reduced PA current
using the power detector (e.g., 730), and terminates the charging.

[0173] In operation 1130, topping charging is performed. Topping charge
may be applied to the battery intermittently, for example, one time per
500 hours. The specific time, current, and voltage values listed above
are merely examples, and other time, current, and voltage values may be
used depending on the particular situation.

[0174] FIG. 12 illustrates an example of a fluctuation in a charging
current. In a graph 1200, an x-axis represents time, and a y-axis
represents a value of charging current. For example, FIG. 12 illustrates
a value of charging current 1210 over time.

[0175] The load (e.g., 890 in FIG. 8) is charged in the CC mode for a
predetermined period of time, for example, 50 minutes. Here, the charging
current may be referred to as a "CC mode reference current." In other
words, the CC mode reference current may indicate the value of the
charging current 1210 when the load is charged in the CC mode. A charging
voltage may be gradually increased to about 4.2 V.

[0176] Subsequently, the charging current 1210 may be gradually reduced to
a range of 20 mA to 30 mA. When a charging mode of the target device
(e.g., 520 in FIG. 5) is changed, the charging current 1210 may have a
predetermined value. A point in time at which the charging current 1210
is reduced to the range of 20 mA to 30 mA may be determined as a charging
termination point. The charging current 1210 may be reduced for a
predetermined period of time, for example 3 hours, and the load may
typically be charged with current of 0.5 C to 1.0 C.

[0177] A CV mode reference current may indicate a value of the charging
current 1210 when a charging mode of the load is regarded to be changed
from the CC mode to the CV mode. A reference current of charging
completion of a target device may indicate a value of the charging
current 1210 when charging of the target device is regarded to be
completed. Additionally, a reference current for removal of a target
device may indicate a value of the charging current 1210 when the target
device is regarded to be removed from charging.

[0178]FIG. 13 illustrates an example of a method of detecting a load for
wireless power transmission and of determining a state of the wireless
power transmission. At step 1310, the source device (e.g., 510 in FIG. 7)
wirelessly transmits a PA power. For example, the control/communication
unit (e.g., 710) determines the PA power. The control/communication unit
controls the power supply (e.g., 720) to adjust a PA supply voltage. The
power supply applies the PA supply voltage to the PA (e.g., 750) based on
the control of the control/communication unit. The PA outputs the
determined PA power. The source resonator (e.g., 760) wirelessly
transmits, to the target device (e.g., 520 in FIG. 8), the PA power.

[0179] For example, a plurality of target devices (e.g., including the
target device 520) may be provided. In this example, a target load may
correspond to a sum of loads (e.g., 890 in FIG. 9) of the plurality of
target devices.

[0180] At step 1320, the control/communication unit detects a change in a
PA current by detecting the PA current. For example, the power detector
(e.g., 730) detects a current of the PA power, namely, the PA current.
The control/communication unit detects the change in the PA current,
using the power detector. For example, when a charging mode of the target
device is changed from a CC charging mode to a CV charging mode, the PA
current may be changed.

[0181] At step 1330, the control/communication unit detects a target load
based on the change in the PA current. At step 1340, the
control/communication unit determines the state of wireless power
transmission based on the detected target load. For example, when the
detected PA current becomes lower than a predetermined value, the
control/communication unit terminates charging of the target device.
Additionally, the control/communication unit adjusts the PA power based
on the detected target load.

[0182] Table 1 shows a relationship between the change in the PA current
detected in step 1320, and the state of the wireless power transmission
determined in step 1340.

TABLE-US-00001
TABLE 1
State of
Change in PA current wireless power transmission
PA current is changed within a A location of a target
predetermined period of time. device may be changed, or
a location of a charging
pad may be changed, or
external effects may occur.
PA current is generated for more than a Charging of a target device
predetermined period of time. may fail, or other problems
may occur.
When a source device is in a single target A currently charged target
device charging mode, or in the CC mode, device may be removed, or
the PA current is reduced. a target device may be
changed from the CC
mode to the CV mode.
When a source device is in a multi-target A currently charged target
device charging mode, the PA current is device may be changed
reduced to a predetermined level. from the CC mode to the
CV mode, or charging of
the target device may be
completed.
When a source device is in the multi-target Whether a target device
device charging mode, the PA current is exists may be determined
reduced to a current corresponding to a via communication between a
target load occurring when there is no source device and a
target device. target device.
When a source device is in the single A target device is added.
target device charging mode, or in
the multi-target device charging
mode, the PA current is increased.
Abnormally high PA current (namely, an An operation of protecting a
overcurrent) is detected. source device is performed.

[0184] Referring to FIG. 14, an electric vehicle charging system 1400
includes a source system 1410, a source resonator 1420, a target
resonator 1430, a target system 1440, and an electric vehicle battery
1450.

[0185] The electric vehicle charging system 1400 may have a similar
structure to the wireless power transmission and charging system of FIG.
1. The source system 1410 and the source resonator 1420 in the electric
vehicle charging system 1400 may function as a source. Additionally, the
target resonator 1430 and the target system 1440 in the electric vehicle
charging system 1400 may function as a target.

[0186] The source system 1410 may include an AC/DC converter, a power
detector, a power converter, a control/communication unit, similarly to
the source device 110 of FIG. 1. The target system 1440 may include a
rectification unit, a DC/DC converter, a switch unit, a charging unit,
and a control/communication unit, similarly to the target device 120 of
FIG. 1.

[0187] The electric vehicle battery 1450 may be charged by the target
system 1440.

[0188] The electric vehicle charging system 1400 may use a resonant
frequency in a band of a few kilohertz (KHz) to tens of MHz.

[0189] The source system 1410 may generate power, based on a type of
charging vehicle, a capacity of a battery, and a charging state of a
battery, and may supply the generated power to the target system 1440.

[0190] The source system 1410 may control the source resonator 1420 and
the target resonator 1430 to be aligned. For example, when the source
resonator 1420 and the target resonator 1430 are not aligned, the
control/communication unit of the source system 1410 may transmit a
message to the target system 1440, and may control alignment between the
source resonator 1420 and the target resonator 1430.

[0191] For example, when the target resonator 1430 is not located in a
position enabling maximum magnetic resonance, the source resonator 1420
and the target resonator 1430 may not be aligned. When a vehicle does not
stop accurately, the source system 1410 may induce a position of the
vehicle to be adjusted, and may control the source resonator 1420 and the
target resonator 1430 to be aligned.

[0192] The source system 1410 and the target system 1440 may transmit or
receive an ID of a vehicle, or may exchange various messages, through
communication.

[0193] The descriptions of FIGS. 2 through 22 may be applied to the
electric vehicle charging system 1400. However, the electric vehicle
charging system 1400 may use a resonant frequency in a band of a few KHz
to tens of MHz, and may transmit power that is equal to or higher than
tens of watts to charge the electric vehicle battery 1450.

[0194] FIGS. 15A through 15B illustrate examples of applications in which
a wireless power receiver and a wireless power transmitter may be
mounted.

[0195] FIG. 15A illustrates an example of wireless power charging between
a pad 1510 and a mobile terminal 1520, and FIG. 15B illustrates an
example of wireless power charging between pads 1530 and 1540 and hearing
aids 1550 and 1560.

[0196] In an example, a wireless power transmitter may be mounted in the
pad 1510, and a wireless power receiver may be mounted in the mobile
terminal 1520. The pad 1510 may be used to charge a single mobile
terminal, namely the mobile terminal 1520.

[0197] In another example, two wireless power transmitters may be
respectively mounted in the pads 1530 and 1540. The hearing aids 1550 and
1560 may be used for a left ear and a right ear, respectively. In this
example, two wireless power receivers may be respectively mounted in the
hearing aids 1550 and 1560.

[0198] FIG. 16A illustrates an example of wireless power charging between
an electronic device 1610 that is inserted into a human body, and a
mobile terminal 1620. FIG. 16B illustrates an example of wireless power
charging between a hearing aid 1630 and a mobile terminal 1640.

[0199] In an example, a wireless power transmitter and a wireless power
receiver may be mounted in the mobile terminal 1620. In this example,
another wireless power receiver may be mounted in the electronic device
1610. The electronic device 1610 may be charged by receiving power from
the mobile terminal 1620.

[0200] In another example, a wireless power transmitter and a wireless
power receiver may be mounted in the mobile terminal 1640. In this
example, another wireless power receiver may be mounted in the hearing
aid 1630. The hearing aid 1630 may be charged by receiving power from the
mobile terminal 1640. Low-power electronic devices, for example Bluetooth
earphones, may also be charged by receiving power from the mobile
terminal 1640.

[0201]FIG. 17 illustrates an example of a wireless power transmitter and
a wireless power receiver.

[0202] In FIG. 17, a wireless power transmitter 1710 may be mounted in
each of the pads 1530 and 1540 of FIG. 15B. Additionally, the wireless
power transmitter 1710 may be mounted in the mobile terminal 1640 of FIG.
16B.

[0203] In addition, a wireless power receiver 1720 may be mounted in each
of the hearing aids 1550 and 1560 of FIG. 15B.

[0204] The wireless power transmitter 1710 may have a similar
configuration to the source device 110 of FIG. 1. For example, the
wireless power transmitter 1710 may include a unit configured to transmit
power using magnetic coupling.

[0205] As illustrated in FIG. 17, the wireless power transmitter 1710
includes a communication/tracking unit 1711. The communication/tracking
unit 1711 may communicate with the wireless power receiver 1720, and may
control an impedance and a resonant frequency to maintain a wireless
power transmission efficiency. Additionally, the communication/tracking
unit 1711 may perform similar functions to the power converter 114 and
the control/communication unit 115 of FIG. 1.

[0206] The wireless power receiver 1720 may have a similar configuration
to the target device 120 of FIG. 1. For example, the wireless power
receiver 1720 may include a unit configured to wirelessly receive power
and to charge a battery. As illustrated in FIG. 17, the wireless power
receiver 1720 includes a target resonator, a rectifier, a DC/DC
converter, and a charging circuit. Additionally, the wireless power
receiver 1720 may include a control/communication unit 1723.

[0207] The communication/control unit 1723 may communicate with the
wireless power transmitter 1710, and may perform an operation to protect
overvoltage and overcurrent.

[0208] The wireless power receiver 1720 may include a hearing device
circuit 1721. The hearing device circuit 1721 may be charged by the
battery. The hearing device circuit 1721 may include a microphone, an
analog-to-digital converter (ADC), a processor, a digital-to-analog
converter (DAC), and a receiver. For example, the hearing device circuit
1721 may have the same configuration as a hearing aid.

[0209] The units described herein may be implemented using hardware
components and software components. For example, the hardware components
may include microphones, amplifiers, band-pass filters, audio to digital
convertors, and processing devices. A processing device may be
implemented using one or more general-purpose or special purpose
computers, such as, for example, a processor, a controller and an
arithmetic logic unit, a digital signal processor, a microcomputer, a
field programmable array, a programmable logic unit, a microprocessor or
any other device capable of responding to and executing instructions in a
defined manner. The processing device may run an operating system (OS)
and one or more software applications that run on the OS. The processing
device also may access, store, manipulate, process, and create data in
response to execution of the software. For purpose of simplicity, the
description of a processing device is used as singular; however, one
skilled in the art will appreciated that a processing device may include
multiple processing elements and multiple types of processing elements.
For example, a processing device may include multiple processors or a
processor and a controller. In addition, different processing
configurations are possible, such a parallel processors.

[0210] The software may include a computer program, a piece of code, an
instruction, or some combination thereof, for independently or
collectively instructing or configuring the processing device to operate
as desired. Software and data may be embodied permanently or temporarily
in any type of machine, component, physical or virtual equipment,
computer storage medium or device, or in a propagated signal wave capable
of providing instructions or data to or being interpreted by the
processing device. The software also may be distributed over network
coupled computer systems so that the software is stored and executed in a
distributed fashion. In particular, the software and data may be stored
by one or more computer readable recording mediums. The computer readable
recording medium may include any data storage device that can store data
which can be thereafter read by a computer system or processing device.
Examples of the non-transitory computer readable recording medium include
read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic
tapes, floppy disks, optical data storage devices. Also, functional
programs, codes, and code segments for accomplishing the example
embodiments disclosed herein can be easily construed by programmers
skilled in the art to which the embodiments pertain based on and using
the flow diagrams and block diagrams of the figures and their
corresponding descriptions as provided herein.

[0211] As a non-exhaustive illustration only, a device described herein
may refer to mobile devices such as a cellular phone, a personal digital
assistant (PDA), a digital camera, a portable game console, and an MP3
player, a portable/personal multimedia player (PMP), a handheld e-book, a
portable laptop PC, a global positioning system (GPS) navigation, a
tablet, a sensor, and devices such as a desktop PC, a high definition
television (HDTV), an optical disc player, a setup box, a home appliance,
and the like that are capable of wireless communication or network
communication consistent with that which is disclosed herein.

[0212] A number of examples have been described above. Nevertheless, it
should be understood that various modifications may be made. For example,
suitable results may be achieved if the described techniques are
performed in a different order and/or if components in a described
system, architecture, device, or circuit are combined in a different
manner and/or replaced or supplemented by other components or their
equivalents. Accordingly, other implementations are within the scope of
the following claims.